Crews of archaeologists and specialized miners completed the removal of 300 tons of soil and rubble beneath Istanbul's Hagia Sophia. The project cleared underground galleries extending 5.6 miles below the atrium of the landmark built in the sixth century AD under Byzantine Emperor Justinian I.
The study, led by Professor Hasan Fırat Diker and published in the journal *Open Archaeology*, cataloged structures dating to the early Byzantine era. Wooden church buildings occupied the site before fires destroyed them, prompting the construction of the stone cathedral between 532 and 537 AD.
Clearing the passages required navigating narrow, dark, and poorly ventilated underground spaces. Three-dimensional mapping revealed a complex network of water conduits alongside subterranean chambers whose original purpose remains under study.
Removal of 300 tons of debris revealed subterranean galleries
Excavating beneath the ancient cathedral atrium required miners trained to handle structural risks and centuries of accumulated debris. As workers cleared the channels, archaeologists identified underground links unknown in earlier surveys.
Previous investigations documented only a few hundred yards of passages. The new survey expanded that network to roughly 5.6 miles of interconnected tunnels beneath Istanbul. Most of the underground structures functioned as aqueducts and drainage systems supporting public supply and church rites in the Byzantine capital.
Among the structures documented by Professor Diker, one chamber contains seven separate water channels. The layering of these conduits shows that workers modified the hydraulic system across different centuries to serve the growing population attending the cathedral.
The mystery of Structure 6 and its eight wall niches
During the cleaning operation, the team identified a passage cataloged as Structure 6. Unlike linear water channels, this section features an irregular layout with branches that end abruptly.
Access to Structure 6 begins at an archway near the junction of two primary tunnels. Beyond the arch, archaeologists cleared a vaulted passage leading to a stone wall not previously recorded on architectural plans of the basilica.
Along one corridor of Structure 6, walls feature eight rectangular niches built under vaulted masonry. The absence of terracotta pipes indicates the passage did not carry water, pointing toward ceremonial use, storage, or underground passage during the Byzantine period.
The role of infrastructure in Constantinople’s ancient cathedral
Built as the central cathedral of the Eastern Roman Empire, Hagia Sophia served as the heart of Byzantine Christianity for more than nine centuries. Following the Ottoman conquest of Constantinople in 1453, the building became a mosque. In 1935 it opened as a museum, and in 2020 the Turkish government reclassified it as a mosque.
The presence of water channels from multiple eras reflects high population density around the cathedral site in Late Antiquity. Water management supported both the maintenance of the vast building and the daily needs of the Christian community.
Historical records regarding urban infrastructure match the physical evidence beneath the site. Subterranean water storage in Constantinople is also evident at the nearby Basilica Cistern, located short distance from Hagia Sophia.
Why are the underground tunnels of Hagia Sophia still being excavated?
Large portions of the tunnel system remain blocked by mud and debris from historical vault collapses. Researchers continue clearing operations to determine whether additional passages link the cathedral to other ancient structures.
Archaeologists are now clearing the remaining sections of Structure 6 to see if the passage originally connected to the Byzantine imperial palace or early church crypts.
Turkey's Ministry of Culture and Tourism oversees the project, ensuring engineering controls protect the structural integrity of the cathedral foundation as workers clear the subterranean galleries.
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